1. Field of the Invention
The present invention relates to a method of forming an armature core of an electric rotating machine. More particularly, the present invention pertains to a method of forming a core sheet used for constituting an armature core.
2. Description of the Prior Art
The armature core of an electric rotating machine has heretofore been formed by one of two different processes. In one process, a multiplicity of separate core sheets are axially stacked. The construction of the typical prior art core sheet is illustrated in FIG. 6A. In accordance with another forming process, the cores of an electric rotating machine are formed by a spirally wound core sheet with an armature rotary shaft press-fitted thereto. Such a conventional spirally wound core sheet is depicted in the prior art drawing of FIG. 6B.
As shown in FIG. 6A, each core sheet 1 which is conventionally used for forming an armature core has the shape of an annular disk, and the radially outer portion of the core sheet 1 is provided with a multiplicity of armature coil winding slots 2 which extend radially inward, are circumferentially spaced at equal intervals and into which armature coils are to be set. The radially inner portion of the core sheet 1 is provided with a multiplicity of relatively long and narrow grooves 3 which extend radially outward. As will be clear from FIG. 6A, each armature coil winding slot 2 formed in the core sheet 1 generally has the shape of the letter "V" and its opening portion 2a is somewhat narrowed. In general, such core sheet 1 is formed of a band-shaped metal sheet 4 such as that shown in FIG. 5. The metal sheet 4 has notches 2' and 3' respectively formed along two longitudinal edges thereof, in advance, the notches 2' and 3' corresponding to the slots 2 and grooves 3 of the core sheet 1, respectively.
The band-shaped metal sheet 4 is formed into the annular disk-shaped core sheet 1 by a process of winding the sheet 4 around a mandrel 5 (see FIG. 2) with one turn. The notches 3' allow the sheet 4 to be bent with no difficulty because they get narrower as the sheet 4 is bent, and with a high degree of accuracy because they engage with projections 6, respectively, which are formed on the mandrel 5.
In the above-described conventional core sheet 1, the grooves 3 which have engaged with the projections 6 on the mandrel 5 remain as shown in FIG. 6A after the process is completed. Accordingly, when an armature rotary shaft (not shown) is press-fitted into the central bore of the core sheet 1 to thereby secure the core sheet 1 to the rotary shaft, such grooves 3 cause a reduction in the area of contact between the core sheet 1 and the armature rotary shaft, resulting in a reduction in the frictional force therebetween thereby inhibiting firm press-fitting of the armature rotary shaft into the central bore of the core sheet 1.
The second prior art embodiment is illustrated in FIG. 6B, showing the spirally wound core sheet 21. As shown in FIG. 6B, the radially outer portion of the core sheet 21 is provided with a multiplicity of armature coil winding slots 22, which extend radially inward, are circumferentially spaced at equal intervals and into which armature coils are to be set. The radially inner portion of the core sheet 21 is provided with a multiplicity of relatively long and narrow grooves 23 which extend radially outward. As will be clear from FIG. 6B, each armature coil winding slot 22 formed in the core sheet 21 generally has the shape of the letter "V" and its opening portion 22a is somewhat narrowed. In general, such a core sheet 21 is formed by a process of spirally winding a band-shaped metal sheet 24 such as that shown in FIG. 5. The metal sheet 4 depicted in FIG. 5 has notches 2' and 3' respectively formed along two longitudinal edges thereof, in advance, the notches 2' and 3' corresponding to the slots 22 and grooves 23 of the core sheet 21, respectively.
The band-shaped metal sheet 4 is formed into the spirally wound core sheet 21 by a process of spirally winding the sheet around a mandrel 5, as illustrated in dotted outline in FIG. 6B. The notches 3' allow the sheet 4 to be bent with no difficulty because they get narrower as the sheet 4 is bent, and with a high degree of accuracy because they engage with projections 6 (FIG. 2), respectively, which are formed on the mandrel 5.
In the above-described conventional core sheet 21, the grooves 23 which have engaged with projections 6 on the mandrel 5 remain as shown in FIG. 6B after the process is completed. Accordingly, when an armature rotary shaft (not shown) is press-fitted into the central bore of the core sheet 21 to thereby secure the core sheet 21 to the rotary shaft, such grooves 23 cause a reduction in the area of contact between the core sheet 21 and the armature rotary shaft, resulting in a reduction in the frictional force therebetween thereby inhibiting firm press-fitting of the armature rotary shaft into the central bore of the core sheet 21.